1. Field of the Invention
This invention relates generally to thermal insulation assemblies and particularly to metallic thermal insulation assemblies such as reflective insulation assemblies used in insulating nuclear reactor applications.
2. Description of the Prior Art
Reflective insulation is used to encase the main body and associated piping of nuclear reactors to minimize heat loss therefrom. Reflective insulation is formed in spaced stacks having a plurality of thin Aluminum or Stainless Steel sheets. These spaced sheets are then encased between thicker and more structurally sound inner and outer cases. The encased stacks are custom formed to the contours of the more rigid inner and outer cases which are formed to conform to the contours of the reactor and associated piping and hence require the joining together of variously contoured encased stacks of reflective insulation of various sizes around the reactor.
Since the heat insulating ability of the stacks depends upon minimizing heat transfer by maintaining spaced zones between the reflective sheets, any compression of the stacks will press the sheets together between the spaced zones impairing the insulating efficiency of the stack. Such compression usually occurs along an edge of the stack when assemblers grab the stack by the end and squeeze together the thin sheets of reflective insulation. To prevent this a strong spacer such as a spacing clip is required to maintain the structural integrity of the stack during the various handling and assembly operations. The spacer also has to support the edge of the stack to prevent the shifting of individual sheets within the stack. Clips are known which provide such a spacing. An example of such clips may be seen in U.S. Pat. No. 4,033,464 entitled "CLIP FOR REFLECTIVE INSULATION." Such clips, however, are localized in their application and usually tie together the edges of the reflective insulation stack. In cases where an initially flat pack of flexible insulation sheets is curved around a body to be insulated a problem may occur when such clips are used. The sheets nearest the curved body to be insulated have a smaller distance to cover than the sheets furthest away. Since the edge of the pack is tied together by the end clips, the sheets nearest the insulated body will tend to corrugate while the sheets furthest from the insulated body will tend to stretch into a straight line between the edge clips since the clip prevents the sheets from overlapping. The result becomes a stack wherein spacing between sheets becomes various in thicknesses and in spots actual contact between certain sheets may occur to short circuit insulation quality.
For maximum insulation efficiency the volume between sheets must also be sealed to eliminate convective heat transfer. Prior art insulation systems used rigid closures to seal the volumes between sheets. An example of such closures may be found in U.S. Pat. No. 3,282,011 entitled "THERMAL INSULATION STRUCTURE." However the closures disclosed therein are rigid and thus eliminate one degree of flexibility of the insulation inner assembly since the inner assembly may not be curved along the rigid closure.
From the foregoing it is seen that there is no prior art reflective insulation assembly which can simultaneously space and seal the individual sheets of reflective insulation while maintaining the required flexibility of the assembly to allow it to be curved around a body without impairing the spacing between sheets or the integrity of the seal between the same sheets.